Video narration
Here’s Raoult’s law in plain terms. Every liquid has a vapor pressure: how strongly its molecules want to escape into the air above it. For an ideal solution, Raoult’s law says the vapor pressure of a component equals its pure vapor pressure times its mole fraction—basically, its share of the mixture. So if a solvent makes up 70% of the liquid, its vapor pressure is about 70% of what it would be if it were pure. Physically, when you dissolve a nonvolatile solute—like salt—in the solvent, fewer solvent molecules are sitting at the surface, so fewer can evaporate. That lowers the solvent’s vapor pressure. Why it matters: vapor pressure controls things like evaporation rate, boiling point, and even humidity over solutions. Raoult’s law gives a simple first model for predicting those changes from composition.